Re: [Libmesh-users] about dofs

[Yujie <rec...@gm...>]

Dear Roy:

Sorry for re-mentioning this problem. I am figuring out how to deal with it.

Our problem is about several Systems with different variable numbers.
Assuming I have 2N Systems. N Systems (Group 1) in them have p variables and
the other N Systems (Group 2) have q variables. Generally, p>q. Because I
need to figure out the corresponding relationship beween variables in Group
1 and 2, that is which variables are from the same discretized physical
points. Therefore, I am wondering how to do it efficiently. If I know the
rules of the Dofs distribution, it should be easy to find their relationship
independing on element looping. do you have any comments about this? thanks
a lot.

Regards,

Yujie



On Thu, Dec 18, 2008 at 7:53 PM, Roy Stogner <roy...@ic...>wrote:

> On Thu, 18 Dec 2008, Yujie wrote:
>
>  Now, I have two System. One has two variables (v1s1,v2s1). The other has
>> one
>> variable (v1s2). They use the same mesh. In parallel mode, what is the
>> ralationship between their dofs?
>> To my knowledge, if I use two cpus and use
>> the variable-major mode and the same shape functions
>>
>
> What is your motivation for wanting to second-guess the DoF indexing
> to begin with?  It's probably not, "I wish my code would break if I
> changed one of the variables' approximation orders", so there's got to
> be some other problem which you're trying to solve.  Whatever that
> problem is, there ought to be a better way to solve it.  Either
> there's a DofObject or DofMap API that can do what you want, and you
> should use it... or there isn't such an API, and we should add it.
>
>  that is, assuming the number of mesh points is n1, if I want to get the
>> relationship between v1s2 and v1s1 in the second cpu, it should be
>> d1_c2_v1s2=d1_c2_v1s1-n1, right? thanks a lot.
>>
>
> Independent Systems have independently indexed DoF coefficient
> vectors; they overlap.  If I'm understanding your notation right, then
> d1_c2_v1s2=d1_c2_v1s1.
> ---
> Roy
>